The typical nuclear reactor core includes a chainreacting nuclear fuel material such as U.sup.235 or U.sup.238 or Pu.sup.239 in the form of pellets encased in separate corrosion resistant heat conductive cans or cladding to form an elongated fuel element referred to as a fuel rod or fuel pin. A number of such fuel elements are grouped together in a pre-arranged spaced matrix within the core of the reactor, with moderators or another form of control means located in a different pre-arranged matrix within the core. The controlled presence of the fuel elements and control means regulate the extent of the nuclear reaction in which neutron bombardment and fission of heavy atoms provides for thermal heating of the fuel elements and surrounding core structures. A reactor coolant is circulated through the core and fuel assemblies and over the fuel elements so as to cool them. Electricity is generated by expansion of the heated coolant using suitable steam expansion equipment.
The fuel element cladding is typically of stainless steel or a zirconium alloy which maintains the fuel material sealed and isolated from the coolant. Failure of the cladding, such as by cracking or localized melting, may result in the release of radioactive fission products which contaminate the circulating coolant and present an operating and safety hazard. It is desirable to identify and locate a leaking fuel element as soon as possible so that the situation can be appraised and fuel replacement procedures quickly initiated with minimal cost and reactor down time.
Gas tagging is a common approach for identifying and locating a leaking fuel element in a nuclear reactor core. In a gas tagging failure detection system, stable isotopes of a gas in proportioned percentages of concentration to one another are sealed within different fuel elements as they are manufactured. The different fuel elements with their unique gas tags are then catalogued according to a prearranged matrix within the core. Upon a breach of a fuel element cladding, the unique "tag gas" mixture escapes to the reactor coolant system. Mass spectrometric analysis of gas samples from the reactor coolant system provides a weighted presence of the isotopes for identifying the unique "tag gas". The corresponding fuel assembly "leaker" may then be identified according to the reactor core's matrix catalog. Examples of this gas tagging approach for diagnosing breached fuel elements can be found in U.S. Pat. Nos. 4,495,143 and 4,764,335.
One of the early difficulties encountered with this gas tagging technique for identifying failed fuel assemblies involved the resolution of multiple, simultaneous failures. A prior art approach developed by the present inventor is described in an article entitled "Barycentric-Coordinates Technique for Identification of Simultaneous Fuel Failures with Gas Tagging," by Kenny C. Gross and Chris Passerello, Nuclear Science and Engineering: 75, 1-11 (1980). This barycentric-coordinates technique (BCT) is capable of resolving simultaneous fuel failures for a relatively small system of gas tags such as, for example, in the Experimental Breeder Reactor-II (EBR-II) with less than 80 unique tags. However, as the number of unique tags in the gas tagging system increases, the number of tag combinations to be searched with the BCT increases exponentially, so that a multi-million dollar supercomputer is required to perform light water reactor (LWR) tagging calculations with more than 750 unique tags.
The present invention addresses the aforementioned limitations of the prior art by providing an expert system and method for identification of simultaneous and sequential fuel failures with gas tagging for use with up to 800 unique gas tags with as many as five simultaneous fuel element failures.